Many farmers can expect a cool and dry spring and possibly drought over summer as scientists are predicting one of the stronger El Nino events on record over the coming months.
NIWA says that based on strong El Nino events going back to the 1970s "an elevated risk for drought for parts of New Zealand is anticipated later during summer".
The risk is particular for eastern parts of both islands as well as northern areas of the North Island, NIWA's Chris Brandolino and Brett Mullan say.
El Nino is certain to continue over the next between September and November and there is a 90 per cent chance it will persist into summer, scientists say.
"The current state of the ocean-atmosphere in the Pacific and the international consensus forecast suggest that this event could rank amongst the four strongest El Nino events recorded."
The others were in 1972-73, 1982-83 and 1997-98.
El Nino events are typically, but not always, associated with stronger and/or more frequent southerwesterly winds during spring. It typically leads to cooler conditions in most areas and wetter conditions to the west of the Southern Alps.
NIWA says rainfall for September, October and November is most likely (a 45-50 percent chance) to be in the below normal range for the north and east of the North Island.
Rainfall totals are about equally likely (35-40 percent chance) to be in the near normal or below normal in the west of the North Island and the north and east of the South Island.
Near normal rainfall is the most likely outcome (45 per cent chance) for the west of South Island.
Temperatures were equally likely (about 40-40 percent chance) to be average or below average from the northern South Island upwards.
Cold snaps and frosts can still be expected in spring.